Low pressure venting panels in accordance with the present invention are often used in conjunction with dust collecting equipment such as bag houses employed to collect milling dust and the like. Such bag houses are subject to the risk of explosion inherent in dust collection and several such catastrophic explosions occur annually in the United States. Bag houses and the like are generally not rigidly constructed and are unable to withstand the force of uncontrolled explosions. Thus, vessels such as bag houses require pressure release safety devices which rupture at relatively low pressure yet predictably rupture so as not to undesirably vent dust into the atmosphere and possibly result in air pollution.
Early devices for providing vent openings in bag houses and the like include burstable membranes or panels of various types, such as roofing paper, cloth, plastic and metal foils. Some membranes or panels are scored to provide lines of weakness; however, reliability, predictability of burst pressure and adequate opening for proper venting was often unsatisfactory.
In other applications requiring a predictable low pressure venting, gaseous processes in large tanks are often subject to explosion or failure. Such tanks are often expensive, the process expensive, and relief devices must be effective and predictable in operation at low pressures. In an effort to provide predicable low pressure rupture panels or discs, two designs have been heretofore developed. A first rupture disc design is termed a composite disc and utilizes a thin floating flexible sealing member in conjunction with a slotted metal member. Here the sealing member is connected to the metal member by its edges but acts independently of the metal member during use. This design has been subject to poor cycling life, relatively inaccurate burst pressures and fragmentation which may clog downstream conduits or provide shrapnel-like projectiles upon violent rupture. Composite discs typically have a central burst point aperture and cut slots or holes to ensure opening in the form of leaves and lack of fragmentation.
A thin very flexible sealing membrane is typically disposed beneath a metal top section. The mechanics of rupture involve swinging out of the metal top section until the thin flexible seal expands uncontrollably and rips open in an undefined tear line. One inherent design deficiency in this type of disc is that the slots in the metal top section greatly weaken the metal and cause the top section to be quite flimsy and move up and down in response to process pressure pulsations. This cycling movement induces fatigue and greatly reduces useful life. The addition of a vacuum support or backing member has done little to alleviate fatigue in the metal sheet.
Further, the use of an independent flexible membrane creates additional problems. The seal tends to creep through the slots in the metal top section when the disc is under pressure. This permits the membrane to balloon and rupture at undesired pressures. Additionally, the pressure of an independent sealing membrane on the metal top section may cause a bulging in the metal top section and an undesired stress on the slots or slits cut in the metal top section which are present to facilitate rupture. This stress may cause the metal top section to deform or to rupture at unpredicted pressures.
A second design of low pressure rupture discs, as is disclosed in the Fike U.S. Pat. No. 4,067,154, uses a solid piece of metal with taped lines and a flexible coating. The burst pressure is determined by the thickness of the metal and the thickness of and type of coating. The tape defines sharp-breaking, shear burst lines to the panel. However, this design is also often believed to yield relatively inaccurate and difficult to predict burst pressures at relatively low bursting pressures. Further, this disc also experiences cycling problems which lead to metal fatigue and premature failure.
The low pressure venting panel of the present invention preferably includes a thin rupture body having a central group of apertures and slits through the body emanating from or from near one or more of the or apertures. A sealing membrane of semi-elastic or relatively inflexible material is bonded to the rupture body at in the area of the slits. This creates a laminated structure which resists expansion in the area of the slits when pressure is applied to the rupture body. Thus, the rupture body resists rupture up to the design limit of the venting panel. The particular venting panel disclosed herein utilizes particular patterns of slits and apertures which have been shown to yield a highly predicable rupture panel. That is, the rupture limit of the venting panel can be predicted in advance and controlled, and the panels can be manufactured with a high degree of certainty as to their rupture limit. It is also desirable in low pressure vent panels to ensure that the panel opens entirely rather than just one of several petals opening. The vent panels of the present application are designed to facilitate full opening of the panel during a typical rupture.